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Example of a GraphAware Transaction-Driven Runtime Module
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/*
 * Copyright (c) 2013-2016 GraphAware
 *
 * This file is part of the GraphAware Framework.
 *
 * GraphAware Framework is free software: you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by the Free Software Foundation, either
 * version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of
 * the GNU General Public License along with this program.  If not, see
 * .
 */

package com.graphaware.example.module;

import com.graphaware.common.util.Change;
import com.graphaware.tx.event.improved.api.ImprovedTransactionData;
import org.neo4j.graphdb.GraphDatabaseService;
import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.Relationship;

import static com.graphaware.common.util.IterableUtils.getSingleOrNull;
import static com.graphaware.example.module.Labels.FriendshipCounter;
import static com.graphaware.example.module.PropertyKeys.STRENGTH;
import static com.graphaware.example.module.PropertyKeys.TOTAL_FRIENDSHIP_STRENGTH;
import static com.graphaware.example.module.Relationships.FRIEND_OF;

/**
 * Example of a Neo4j {@link org.neo4j.graphdb.event.TransactionEventHandler} that uses GraphAware {@link ImprovedTransactionData}
 * to do its job, which is counting the total strength of all friendships in the database and writing that to a special
 * node created for that purpose.
 */
public class FriendshipStrengthCounter {

    private final GraphDatabaseService database;

    public FriendshipStrengthCounter(GraphDatabaseService database) {
        this.database = database;
    }

    public void handleCreatedFriendships(Iterable createdRelationships) {
        long delta = 0L;

        for (Relationship newFriendship : createdRelationships) {
            if (newFriendship.isType(FRIEND_OF)) {
                delta += (long) newFriendship.getProperty(STRENGTH, 0L);
            }
        }

        applyDelta(delta);
    }

    public void handleChangedFriendships(Iterable> changedRelationships) {
        long delta = 0L;

        for (Change changedFriendship : changedRelationships) {
            if (changedFriendship.getPrevious().isType(FRIEND_OF)) {
                delta -= (long) changedFriendship.getPrevious().getProperty(STRENGTH, 0L);
                delta += (long) changedFriendship.getCurrent().getProperty(STRENGTH, 0L);
            }
        }

        applyDelta(delta);
    }

    public void handleDeletedFriendships(Iterable deletedRelationships) {
        long delta = 0L;

        for (Relationship deletedFriendship : deletedRelationships) {
            if (deletedFriendship.isType(FRIEND_OF)) {
                delta -= (long) deletedFriendship.getProperty(STRENGTH, 0L);
            }
        }

        applyDelta(delta);
    }

    private void applyDelta(long delta) {
        if (delta != 0L) {
            Node root = getCounterNode(database);
            root.setProperty(TOTAL_FRIENDSHIP_STRENGTH, (long) root.getProperty(TOTAL_FRIENDSHIP_STRENGTH, 0L) + delta);
        }
    }

    /**
     * Get the counter node, where the friendship strength is stored. Create it if it does not exist.
     *
     * @param database to find the node in.
     * @return counter node.
     */
    private static Node getCounterNode(GraphDatabaseService database) {
        Node result = getSingleOrNull(database.findNodes(FriendshipCounter));

        if (result != null) {
            return result;
        }

        return database.createNode(FriendshipCounter);
    }

    /**
     * Get the counter value of the total friendship strength counter.
     *
     * @return total friendship strength.
     */
    public long getTotalFriendshipStrength() {
        return (long) getCounterNode(database).getProperty(TOTAL_FRIENDSHIP_STRENGTH, 0L);
    }
}